The present invention relates to actuators. More particularly, the present invention relates actuators used in closed loop flow systems in aircraft and gas turbine engines.
Aircraft and gas turbine engines utilize various actuators to drive aircraft or engine structures to desired positions. For example, aircraft utilize linear actuators to move flight control surfaces such as flaps, slates, and spoilers. In gas turbine engines, actuators are used, for example, to rotate struts to desired positions and open and close bleed doors.
Unfortunately, many aircraft and gas turbine engine structures must be designed to be larger, heavier, and more structurally sound than would otherwise have been required in the absence of the linear actuators driving them. This “over-sizing” of the structures results from a failure to adequately control the load output of the actuators. More particularly, many actuators rely on closed loop flow systems that do not adequately account for inertia of the fluid in the system. The inertia of the fluid becomes problematic when the structure(s) being actuated reaches a structural stop (e.g., a closed position). As a result of inertia fluid effects, the actuator exerts a load on the structure that exceeds desired limits. Repeatedly exceeding desired loads can cause excessive wear and failure of the actuator, connecting linkages, and structures being actuated.